CN108700230B - Threaded joints for steel pipes - Google Patents

Abstract

Nipple is made of pin thread (10) and female thread (20).Pin thread (10) successively has the 1st external thread part (11), the 1st sealing surface (12), circular bead surface (13), the 2nd sealing surface (14) and the 2nd external thread part (15) from the top of pin thread (10) towards pipe main body.Female thread (20) has the 1st internal thread part (21), the 1st sealing surface (22), circular bead surface (23), the 2nd sealing surface (24) and the 2nd internal thread part (25).Distance (L1) until from the boundary (P1) of the 1st sealing surface (12,22) to the position (P3) of circular bead surface (13,23) and the distance (L2) until the boundary (P2) to position (P3) of the 2nd sealing surface (14,24) are 15mm or more respectively, and total distance (L) of distance (L1) and distance (L2) is 50mm or more.Nipple can play excellent sealing performance as a result,.

Description

Threaded joints for steel pipes

technical field

The present invention relates to threaded joints for joining steel pipes.

Background technique

In oil wells, natural gas wells, and the like (hereinafter collectively referred to as "oil wells"), steel pipes called oil country tubular goods (OCTG: Oil Country Tubular Goods) are used in order to exploit underground resources. The steel pipes are connected in turn, and the connection uses threaded joints.

The form of threaded joints for steel pipes is roughly divided into combination type and integral type. In the case of a combined type, one of a pair of pipe materials to be connected is a steel pipe, and the other pipe material is a pipe joint. In this case, external thread portions are formed on the outer peripheries of both end portions of the steel pipe, and internal thread portions are formed on the inner peripheries of both end portions of the pipe joint. And, the steel pipe is connected to the pipe joint. In the case of integral type, the pair of pipes to be connected are both steel pipes, and no additional joints are used. In this case, an external thread portion is formed on the outer periphery of one end portion of the steel pipe, and an internal thread portion is formed on the inner periphery of the other end portion. And, one steel pipe is connected with another steel pipe.

Generally, the joint portion of the pipe end on which the male thread is formed includes an element to be inserted into the female thread, so it is called a pin. On the other hand, the joint portion of the pipe end in which the female thread portion is formed is called a box because it includes an element for accommodating the male thread portion. These pins and boxes are the ends of the tubing and are therefore tubular.

In recent years, oil wells are being developed to a higher depth and to an ultra-deep sea. Under such circumstances, in order to efficiently develop oil wells, oil well tubulars are arranged in multiple layers. A threaded joint in which the outer diameter of the box and the outer diameter of the pin is at the same level is often used for the connection of multi-layered oil well pipes. The reason for this is that since a gap is required between the inner oil well tubular and the outer oil well tubular in the multilayer structure, the expansion of the outer diameter of the inner oil well tubular box is limited by the inner diameter of the outer oil well tubular pin. Under such constraints, threaded joints are required to have excellent sealing performance against internal pressure (hereinafter, also referred to as "internal pressure") and external pressure (hereinafter, also referred to as "external pressure").

For example, there is a threaded joint in which a dovetail-shaped tapered thread also called a wedge thread is used as a threaded joint that achieves excellent sealing performance. In the wedge thread, the tooth profile half angles of the load flank (hereinafter, also referred to as "load surface") and the insertion flank (hereinafter, also referred to as "insertion surface") are both negative angles, and when the fastening is completed, The load faces are in contact with each other and the insertion faces are in contact with each other. Thereby, the whole thread part is firmly fitted. In addition, in the fastened state, the crest surface of the thread portion and the bottom surface of the thread groove are in contact with each other and closely adhered to each other. In this way, the threaded joint using the wedge thread can achieve excellent sealing performance because there is no gap in the threaded portion.

U.S. Patent No. 7,690,696 (Patent Document 1) and U.S. Patent Application Publication No. 2006/0145480 (Patent Document 2) disclose threaded joints in which wedge-shaped threads are used for the threaded portion.

In the threaded joint of Patent Document 1, the threaded portion is divided into two along the pipe axis, and a shoulder portion is provided at the boundary between the two threaded portions. Adjacent to this shoulder, a seal based on surface contact is provided. In the threaded joint of Patent Document 1, the sealing performance is improved by utilizing the locking effect of the combination of the fit and closeness of the wedge-shaped thread without gaps and the pressing contact between the shoulder surfaces.

However, in the case of the threaded joint of Patent Document 1, in order to achieve close contact without gaps in a fastened state, the tolerance of the design dimensions set for either the thread portion or the shoulder portion of the wedge screw becomes small. . As a result, not only does the manufacturing cost increase, but also the machining dimension deviates from the tolerance. If the tolerance deviates, the locking effect cannot be fully exhibited, and there is a possibility that the expected sealing performance cannot be obtained.

On the other hand, in the case of the threaded joint of Patent Document 2, similarly to the threaded joint of Patent Document 1, a shoulder portion and a seal portion are provided at the boundary between the two-stage threaded portions. Also, in any one of the two-stage threaded portions, gaps are formed between load surfaces, between insertion surfaces, between thread crest surfaces and thread groove bottom surfaces, and the like. According to such a structure, the tolerance of the design dimension set with respect to a thread part will become large. Thereby, the manufacturing cost can be reduced, and it is easy to make the processing dimension within the tolerance.

However, in the case of the threaded joint of Patent Document 2, only one sealing portion by surface contact is provided. Therefore, in the case where excessive pressure (internal pressure and external pressure) is applied to the threaded joint, there is a possibility that the sealing performance cannot be maintained. In particular, in the case of a threaded joint in which the outer diameter of the box is approximately the same as that of the pin, it is difficult to ensure sealing performance because the expansion of the wall thickness of the pin and box is limited.

prior art literature

patent documents

Patent Document 1: Specification of U.S. Patent No. 7,690,696

Patent Document 2: Specification of US Patent Application Publication No. 2006/0145480

Contents of the invention

The problem to be solved by the invention

An object of the present invention is to provide a threaded joint for steel pipes capable of reliably exhibiting excellent sealing performance.

solutions to problems

A threaded joint for steel pipes according to an embodiment of the present invention is a threaded joint for steel pipes consisting of a tubular pin and a tubular box, and the pin and the box are fastened by screwing the pin into the box. Referring to the box, the threaded joint for steel pipes includes the following structures.

(1) The outer diameter of the female snap is less than 110% of the outer diameter of the pipe body of the male snap.

(2) The pin has a first external thread portion of a dovetail-shaped tapered thread, a first sealing surface, a shoulder surface, a second sealing surface, and a dovetail-shaped tapered thread in order from the tip of the pin toward the pipe body. The second external thread part.

(3) The first sealing surface has a first tapered surface and first curved surfaces at both ends of the first tapered surface. The second sealing surface has a second tapered surface and second curved surfaces at both ends of the second tapered surface. A distance L1 in the pipe axis direction from a boundary between the first tapered surface and the first curved surface on the distal end side of the pin to the shoulder surface is 15 mm or more. A distance L2 in the tube axis direction from the boundary between the second tapered surface and the second curved surface on the tube body side of the pin to the shoulder surface is 15 mm or more. The total distance L of the distance L1 and the distance L2 is 50 mm or more.

(4) The box has a first internal thread portion of a dovetail-shaped tapered thread, a first sealing surface, a shoulder surface, a second sealing surface, and a dovetail-shaped tapered thread in order from the pipe body of the box toward the tip. The second internal thread part.

(5) In the tightened state, in the above-mentioned threaded joint,

The shoulder surfaces are in contact with each other, the first sealing surfaces are in contact with each other, and the second sealing surfaces are in contact with each other,

A gap is formed between the insertion flanks of the first external thread portion and the first internal thread portion, and a gap is formed between the bottom surface of the thread groove of the first external thread portion and the first internal thread portion. A gap is formed between crest surfaces of threads or between a crest surface of the first externally threaded portion and a bottom surface of a thread groove of the first internally threaded portion,

· A gap is formed between the insertion flanks of the second externally threaded portion and the second internally threaded portion, and a gap is formed between the bottom surface of the thread groove of the second externally threaded portion and the A gap is formed between crest surfaces of threads or between a crest surface of the second externally threaded portion and a bottom surface of a thread groove of the second internally threaded portion.

In the above threaded joint, preferably, the gap between the crest surface of the thread and the bottom surface of the thread groove is 0.10 mm or more and less than 0.20 mm.

In the above-mentioned threaded joint, it is preferable to have a structure in which the angle formed by the pipe axis and the shoulder surface is 75° to 105° in a longitudinal section along the pipe axis.

In the threaded joint described above, it is preferable that the total distance L is 90 mm or less.

In the threaded joint described above, it is preferable that the first threaded portion constituted by the first externally threaded portion and the first internally threaded portion and the second externally threaded portion and the second internally threaded portion The second thread part constituted is one thread or two threads.

The effect of the invention

The threaded joint for steel pipes of the present invention has the following remarkable effects:

Can reliably exhibit excellent sealing performance.

Description of drawings

Fig. 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to an embodiment of the present invention.

Fig. 2 is an enlarged longitudinal sectional view of the vicinity of the boundary between two threaded portions in the threaded joint for steel pipes shown in Fig. 1 .

Fig. 3 is an enlarged longitudinal sectional view of a first threaded portion of the threaded joint for steel pipes shown in Fig. 1 .

Fig. 4 is an enlarged longitudinal sectional view of a second threaded portion of the threaded joint for steel pipes shown in Fig. 1 .

Fig. 5 is a diagram showing the dimensional relationship between the first sealing surface and the shoulder surface in the male snap according to the present embodiment.

Fig. 6 is a diagram showing the dimensional relationship between the second sealing surface and the shoulder surface in the male snap according to the present embodiment.

Fig. 7 is a longitudinal sectional view schematically showing a region of an inner seal portion by surface contact.

Fig. 8 is a longitudinal sectional view schematically showing a region of an outer seal portion by surface contact.

Detailed ways

As described above, in the threaded joint for steel pipes, since the expansion of the outer diameter of the box is limited, a threaded joint in which the outer diameter of the box is on the same level as the outer diameter of the pin is often used. In such threaded joints, in order to ensure sealing performance, a sealing portion based on surface contact is often provided.

In a conventional threaded joint, for example, an inner seal portion is provided at the tip end of the pin, and an outer seal portion is provided at the tip end portion (the side of the box opposite to the pipe body side of the box) of the box. Since the inner seal portion is close to the inside, the inner seal portion mainly contributes to the sealing performance against internal pressure. Since the outer seal portion is close to the outside, the outer seal portion mainly contributes to the sealing performance against external pressure. In addition, two stages of threaded portions are provided in a region between the inner seal portion and the outer seal portion. Furthermore, a shoulder portion is provided at the boundary between the two stages of threaded portions. The threaded part adopts, for example, a buttress-shaped tapered thread.

In the conventional threaded joint having such a structure, the wall thicknesses of the pin and the box are thinned in the area of the seal portion (the inner seal portion and the outer seal portion). The reason for this is that it is necessary to provide a sealing portion at the respective tip portions of the pin and the box while securing the dangerous cross-sectional area of the pin and the box. Here, the critical cross section is a cross section located at the end of the engagement region of the threaded portion and where the cross sectional area bearing the tensile load is the smallest. The location of the critical section and its cross-sectional area are elements used to determine the tensile strength of a threaded joint.

If the wall thickness of the sealing part area is thin, when excessive pressure (internal pressure and external pressure) is applied to the threaded joint, the sealing part area may be excessively deformed, and the sealing performance may not be maintained.

In contrast, the threaded joint of Patent Document 2 can suppress excessive deformation of the sealing portion region when pressure is applied. The reason for this is that, in the threaded joint of Patent Document 2, since the sealing portion is provided adjacent to the shoulder portion at the boundary of the two-stage threaded portions, it is possible to secure the wall thickness of the pin and the box in the region of the sealing portion. thick.

In addition, in the case of the threaded joint of Patent Document 2, a dovetail-shaped thread portion is employed. In any one of the two-stage threaded portions, gaps are formed between the load surfaces, between the insertion surfaces, between the crest surface and the bottom surface of the thread groove, and the like. That is, the threaded portion does not fit closely without gaps over the entire area.

Here, in the case of a threaded joint having a threaded portion of a wedge-shaped thread without clearance (for example: the threaded joint of the aforementioned Patent Document 1), there are the following problems. At the time of fastening, the fitting and closeness of the threaded portion occurs earlier than the butt ring (Japanese: ショルダリング) (shoulder surfaces abut against each other). Therefore, the tightening torque becomes excessive at the time of butting, and the tightening operation fails. In addition, when the fastening is completed, the threaded portion is already sufficiently engaged, and the load cannot be sufficiently borne by the shoulder portion. Therefore, damage to the threaded portion increases.

On the other hand, regarding the above-mentioned threaded joint having a dovetail-shaped threaded portion with a gap, specifically, a threaded portion having a gap between the insertion surfaces and a gap between the crest surface and the bottom surface of the thread groove When tightening a threaded joint, the plastic deformation of the threaded part is delayed for a time corresponding to the existing gap, so that the shoulder part can fully bear the load.

Therefore, a threaded joint having a threaded portion with a gap can exhibit superior sealing performance compared to a threaded joint having a threaded portion without a gap.

However, even in a threaded joint having a threaded portion with a gap, in a threaded joint to which excessive internal pressure and external pressure are applied, it is preferable not to provide a sealing portion at only one place (see Patent Document 2). threaded joints), but separately provide the inner seal part for internal pressure and the outer seal part for external pressure. The reason for this is that the internal pressure and the external pressure can be effectively shared by the provision of the individual sealing parts, and the sealing performance can be further ensured.

In this regard, in the threaded joint of Patent Document 2, as described above, only one sealing portion is provided adjacent to the shoulder portion. Assuming that two seals are to be provided in the threaded joint of Patent Document 2, an inner seal and an outer seal are provided adjacent to the shoulder on both sides sandwiching the shoulder. In this case, the inner seal portion and the outer seal portion are close to each other.

However, in the case of a threaded joint in which the inner seal and the outer seal are close together, the contact of the inner seal and the contact of the outer seal interact with each other during tightening, and the respective sealing surfaces cannot be sufficiently fitted together. . Therefore, the interference amount (interference amount) of each sealing portion becomes insufficient, and the sealing performance cannot be exerted on the contrary.

Therefore, the state where the inner seal portion and the outer seal portion are close is not appropriate, and it is necessary to extend the distance between the inner seal portion and the outer seal portion to a certain extent. If the distance between the inner seal portion and the outer seal portion is ensured, the interaction between the contact of the inner seal portion and the contact of the outer seal portion during fastening is relaxed. As a result, the fitting and close contact between the respective sealing surfaces becomes sufficient, and excellent sealing performance can be reliably exhibited.

In addition, as the distance between the inner seal portion and the outer seal portion is ensured, in the pin and the box, a rigid body portion having a sufficient length is formed between the two seal portions, respectively. The rigid portion functions to expand or contract the diameter of the sealing portion in the same manner when pressure is applied. Utilizing this action, occurrence of warping on each sealing surface is suppressed, and improvement of sealing performance can be expected.

However, at first glance, when an excessive compressive load is applied to the threaded joint, the respective sealing surfaces of the inner seal portion and the outer seal portion are separated from each other along the pipe axis direction, and there is concern about a decrease in sealing performance. However, since the shoulder portion is disposed between the inner seal portion and the outer seal portion, and the shoulder portion bears the compressive load, the seal surfaces are not separated from each other along the pipe axis direction, and the sealing performance is not lowered.

The threaded joint for steel pipes of the present invention is completed based on the above knowledge. Embodiments of the threaded joint for steel pipes according to the present invention will be described below.

Fig. 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to an embodiment of the present invention. Fig. 2 is an enlarged longitudinal sectional view of the vicinity of the boundary between two threaded portions in the threaded joint for steel pipes shown in Fig. 1 . As shown in FIGS. 1 and 2 , the threaded joint of this embodiment is an integral threaded joint, which is composed of a pin 10 and a box 20 . However, the threaded joint of this embodiment can also be applied to a combination type threaded joint.

The threaded joint of the present embodiment is aimed at a threaded joint in which the outer diameter of the box 20 is approximately the same as the outer diameter of the pin 10 . Therefore, the outer diameter of the box 20 is 100% or more and less than 110% of the outer diameter of the pipe body of the pin 10 .

The male snap 10 includes a first external thread portion 11 , a first sealing surface 12 , a shoulder surface 13 , a second sealing surface 14 , and a second external thread portion 15 in order from the distal end side of the male snap 10 toward the pipe main body. Both the first sealing surface 12 and the second sealing surface 14 are tapered. Strictly speaking, the first sealing surface 12 and the second sealing surface 14 each have a shape corresponding to the peripheral surface of a circular truncated cone whose diameter decreases toward the tip side of the pin 10, or have a shape corresponding to the peripheral surface of the circular truncated cone. The shape is a combination of a surface and a surface corresponding to the peripheral surface of a rotating body obtained by rotating a curved line such as an arc around the pipe axis CL.

The shoulder surface 13 is an annular surface substantially perpendicular to the pipe axis CL. In FIGS. 1 and 2 , a state in which the shoulder surface 13 is slightly tilted from the direction in which the male snap 10 is screwed in, which is perpendicular to the pipe axis CL, is shown. In other words, it shows a state in which the shoulder surface 13 is slightly tilted toward the front end side of the male buckle 10 as the shoulder surface 13 is on the outer peripheral side.

On the other hand, the box 20 includes a first internally threaded portion 21 , a first sealing surface 22 , a shoulder surface 23 , a second sealing surface 24 , and a second internally threaded portion 25 in order from the pipe body side of the box 20 toward the distal end. . The first internal thread portion 21, the first sealing surface 22, the shoulder surface 23, the second sealing surface 24, and the second internal thread portion 25 of these female snaps 20 are respectively set to the first external thread portion 11, The first sealing surface 12, the shoulder surface 13, the second sealing surface 14, and the second external thread portion 15 correspond to each other.

The first external thread portion 11 of the pin 10 and the first internal thread portion 21 of the box 20 are dovetail-shaped tapered threads that engage with each other, and constitute a first thread portion (inner thread portion) close to the inside. The second external thread portion 15 of the pin 10 and the second internal thread portion 25 of the box 20 are also dovetail-shaped tapered threads that engage with each other, and constitute a second thread portion (outer thread portion) near the outside.

3 and 4 are longitudinal cross-sectional views enlarging the threaded portion of the threaded joint for steel pipes shown in FIG. 1 . 3 shows the first threaded portion, and FIG. 4 shows the second threaded portion.

As shown in FIG. 3, regarding the inner threaded portion, the first external threaded portion 11 of the pin 10 has a thread crest surface 11a, a thread groove bottom surface 11b, and an insertion flank 11c (hereinafter, also referred to as the thread surface 11c) that precedes the screwing process. is an "insertion surface") and a load flank 11d (hereinafter also referred to as a "load surface") opposite to the insertion surface 11c. On the other hand, the first internally threaded portion 21 of the box 20 has a thread crest surface 21a opposing the thread groove bottom surface 11b of the first externally threaded portion 11 , and a thread crest surface 21a opposing the thread crest surface 11a of the first externally threaded portion 11 . The thread groove bottom surface 21 b , the insertion surface 21 c facing the insertion surface 11 c of the first male thread portion 11 , and the load surface 21 d facing the load surface 11 d of the first male thread portion 11 .

As shown in FIG. 4, regarding the external threaded portion, the second external threaded portion 15 of the pin 10 has a thread crest surface 15a, a thread groove bottom surface 15b, an insertion surface 15c that precedes the screw-in process, and the insertion surface 15c. The load surface 15d on the opposite side. On the other hand, the second internally threaded portion 25 of the box 20 has a thread crest surface 25 a facing the thread groove bottom surface 15 b of the second externally threaded portion 15 , and a thread crest surface 25 a facing the thread crest surface 15 a of the second externally threaded portion 15 . The thread groove bottom surface 25 b , the insertion surface 25 c facing the insertion surface 15 c of the second male thread portion 15 , and the load surface 25 d facing the load surface 15 d of the second male thread portion 15 .

The profile half angles of the load surfaces 11d, 21d and insertion surfaces 11c, 21c of the first thread portion and the load surfaces 15d, 25d, insertion surfaces 15c, 25c of the second thread portion are all negative angles smaller than 0°. Here, the half-angle of the profile is the angle formed by the surface at right angles to the pipe axis CL and the tooth flank. In the case of the threaded joints shown in Figures 3 and 4, the half-angles of the tooth profiles on the loading surfaces 11d, 21d, 15d, and 25d are positive in the clockwise direction, and the half-angles of the tooth profiles on the insertion surfaces 11c, 21c, 15c, and 25c are in the counterclockwise direction. is positive.

The first external threaded part 11 and the first internal threaded part 21 (inside threaded part) and the second external threaded part 15 and the second internal threaded part 25 (outside threaded part) can be screwed into each other respectively, and are embedded in each other in a fastened state. Close and close together, become the state of interference fit. The first sealing surfaces 12 , 22 and the second sealing surfaces 14 , 24 come into contact with each other as the pin 10 is screwed in, and are fitted closely in a fastened state to form an interference fit state. As a result, the first sealing surfaces 12 and 22 form a first sealing portion (inner sealing portion) based on surface contact. The second sealing surfaces 14 and 24 form a second sealing portion (outer sealing portion) based on surface contact.

The shoulder surfaces 13 and 23 contact each other and are pressed as the pin 10 is screwed in, and function as stoppers that limit the screwing of the pin 10 . The shoulder surfaces 13 and 23 form shoulder portions by such mutual pressing contact, and function as stoppers. When the shoulder surfaces 13 and 23 are in the tightened state, the load surfaces 11d and 15d of the pin 10 of the first threaded part and the second threaded part respectively apply the so-called tightening axial force of the screw thread, and act as a load by its reaction. The action of the load produced by the force.

Regarding the internally threaded portion in the fastened state, the load surface 11d of the first externally threaded portion 11 and the load surface 21d of the first internally threaded portion 21 are in contact with each other. In addition, the thread crest surface 11 a of the first external thread portion 11 and the thread groove bottom surface 21 b of the first internal thread portion 21 are in contact with each other. Furthermore, a gap is formed between the insertion surface 11c of the first external thread portion 11 and the insertion surface 21c of the first internal thread portion 21 . A gap is formed between the thread groove bottom surface 11 b of the first external thread portion 11 and the thread crest surface 21 a of the first internal thread portion 21 . However, it is also conversely possible that the thread groove bottom surface 11b of the first externally threaded portion 11 and the thread crest surface 21a of the first internally threaded portion 21 are in contact with each other and the crest surface 21a of the first externally threaded portion 11 is in contact with each other. 11a and the thread groove bottom surface 21b of the first internally threaded portion 21 in such a manner that a gap is formed.

Regarding the externally threaded portion in the fastened state, the load surface 15d of the second externally threaded portion 15 and the load surface 25d of the second internally threaded portion 25 are in contact with each other. In addition, the thread groove bottom surface 15b of the second external thread portion 15 and the thread crest surface 25a of the second internal thread portion 25 are in contact with each other. Furthermore, a gap is formed between the insertion surface 15 c of the second external thread portion 15 and the insertion surface 25 c of the second internal thread portion 25 . A gap is formed between the thread crest surface 15 a of the second external thread portion 15 and the thread groove bottom surface 25 b of the second internal thread portion 25 . However, it is also conversely possible that the thread crest surface 15a of the second externally threaded portion 15 and the thread groove bottom surface 25b of the second internally threaded portion 25 are in contact with each other and the thread groove bottom surface 15b of the second externally threaded portion 15 is in contact with each other. There is a form in which a gap is formed with the thread crest surface 25 a of the second female thread portion 25 .

Fig. 5 is a diagram showing the dimensional relationship between the first sealing surface and the shoulder surface in the male snap according to the present embodiment. As shown in FIG. 5 , the first sealing surface 12 of the male snap 10 has a first tapered surface 12a and first curved surfaces 12b, 12c. The first curved surfaces 12b and 12c exist at both ends of the first tapered surface 12a. The position P1 is the boundary between the first tapered surface 12 a and the first curved surface 12 c on the tip side of the pin 10 . The position P3 is the position of the maximum diameter of the shoulder surface 13 of the pin 10 . The distance L1 in the pipe axis CL direction from the position P1 to the position P3 is 15 mm or more.

Fig. 6 is a diagram showing the dimensional relationship between the second sealing surface and the shoulder surface in the male snap according to the present embodiment. As shown in FIG. 6, the second sealing surface 14 of the male snap 10 has a second tapered surface 14a and second curved surfaces 14b, 14c. Second curved surfaces 14b and 14c exist at both ends of the second tapered surface 14a. The position P2 is the boundary between the second tapered surface 14 a and the second curved surface 14 b on the pipe main body side of the pin 10 . The distance L2 in the pipe axis CL direction from the position P2 to the position P3 is 15 mm or more. Furthermore, the total distance L of the distance L1 and the distance L2 is 50 mm or more.

In short, in the present embodiment, the inner sealing portion (first sealing portion) is formed by surface contact between the first sealing surface 12 of the pin 10 and the first sealing surface 22 of the box 20 . The position of the inner seal portion is defined by a position P1 that is a boundary between the first tapered surface 12 a and the first curved surface 12 c of the first sealing surface 12 of the pin 10 . The position of the outer seal portion (second seal portion) is defined by a position P2 that is a boundary between the second tapered surface 14 a and the second curved surface 14 b of the second seal surface 14 of the pin 10 . Furthermore, a shoulder portion is disposed between the inner seal portion and the outer seal portion. The position of the shoulder portion is defined by the position P3 of the shoulder surface 13 of the pin 10 . In addition, the distance in the direction of the tube axis between the inner seal and the outer seal corresponds to the distance L1 from the position P1 of the inner seal to the position P3 of the shoulder and the distance L1 from the position P2 of the outer seal to the shoulder. The total distance L of the distance L2 up to the position P3 has a certain length.

In addition, as shown in FIG. 2 , the male snap 10 and the female snap 20 have a gap C1 formed between the inner seal portion and the shoulder portion, and are not in contact with each other. Similarly, the male buckle 10 and the female buckle 20 have a gap C2 formed between the outer seal portion and the shoulder portion, and are not in contact with each other.

In this way, in the threaded joint for steel pipes according to this embodiment, the inner seal portion, the shoulder portion, and the outer seal portion are sequentially provided between the dovetail-shaped thread portion divided into two regions, thereby ensuring the smoothness from the inner seal portion to the outer seal portion. distance to the seal. In addition, in the threaded portion, there is a gap between the insertion surfaces, and a gap between the crest surface of the thread and the bottom surface of the thread groove. By employing such a structure, the threaded joint of the present embodiment reliably exhibits excellent sealing performance against internal pressure and external pressure.

Hereinafter, preferred aspects of the main parts will be supplemented.

[Distance L between inner seal and outer seal]

The distance L between the inner seal portion and the outer seal portion is 50 mm or more. If the distance L is less than 50 mm, the contact of the inner seal part and the contact of the outer seal part interact with each other during fastening, and the sealing performance cannot be exerted on the contrary. A preferable lower limit of the distance L is 55 mm.

On the other hand, the upper limit of the distance L is not particularly defined. However, if the distance L is too long, the following disadvantages will occur. Since the overall length of the joint portion increases, the manufacturing cost increases. In addition, since the area where pressure is applied increases as the overall length of the joint portion increases, the joint portion is prone to plastic deformation, and there is a risk of fracture in a corrosive environment. Therefore, in order to avoid these disadvantages, the preferable upper limit of the distance L is 90 mm. A more preferable upper limit of the distance L is 80 mm.

[Distances L1, L2 from the seal portion (inner seal portion and outer seal portion) to the shoulder portion]

The distance L1 from the inner seal to the shoulder and the distance L2 from the outer seal to the shoulder are set in relation to the distance L between the inner seal and the outer seal, and both are set to More than 15mm. If the distances L1 and L2 are less than 15 mm, it will be difficult to secure the sealing surface. The preferable lower limit of distance L1, L2 is 20 mm.

[the shoulder part]

In a longitudinal section along the tube axis, it is preferable that the angle formed by the tube axis and the shoulder surface is 75° to 105°. If the angle is less than 75°, the shoulder surfaces are in a state of being pressed into contact with each other in a hook-like form while being largely tilted from the direction perpendicular to the pipe axis toward the screwing-in progress of the pin. Therefore, the shoulder portion is easily deformed plastically, and the sealing performance becomes unstable. A more preferable lower limit of the angle of the shoulder surface is 85°.

On the other hand, if the angle exceeds 105°, the shoulder surfaces are largely tilted from the surface perpendicular to the pipe axis in the direction opposite to the direction in which the pin is screwed in. Therefore, as the shoulder surfaces are pressed into contact with each other, the force of reducing the diameter acts on the pin, and at the same time, the force of expanding the diameter acts on the box, so that the contact surface pressure between the sealing surfaces decreases. A more preferable upper limit of the angle of the shoulder surface is 95°. Furthermore, the optimal angle of the shoulder surface is 90°. The reason for this is that when the angle of the shoulder surface is 90°, the sealing performance is stable and the processing of the shoulder portion becomes easy.

If the width of the shoulder surface of the pin and the box is too small, the load cannot be fully supported, and the compression resistance performance is reduced. Therefore, the width of the shoulder surface of the pin and box is preferably 10% or more, more preferably 15% or more, of the wall thickness of each pipe body.

[Seal (inner seal and outer seal)]

In the region of the sealing portion, if either the pin or the box is too thick, the thickness of the other becomes thinner correspondingly, and the rigidity of the other decreases. The pressure resistance performance of the pin or box with reduced stiffness is reduced. Therefore, it is preferable that the wall thickness of the pin and the box in the region of the sealing portion be 45% or more and 80% or less of the wall thickness of the respective pipe main bodies. The preferable lower limit of each wall thickness is 10.5 mm. The preferred upper limit of the respective wall thickness is 17 mm.

If the tapered slope of the sealing surface is too sharp, the sealing performance will decrease when a tensile load is applied. On the other hand, if the inclination of the taper of the sealing surface is too gentle, the entire length of the sealing portion increases, which increases the manufacturing cost. Therefore, it is preferable that the taper angle of the sealing surface is 2° to 10° with respect to the pipe axis. A more preferable lower limit of the taper angle of the sealing surface is 3°. A more preferable upper limit of the taper angle of the sealing surface is 7°.

[Threaded part (inner threaded part and outer threaded part)]

If the inclination of the taper of the thread portion is too steep, the length of the entire thread portion becomes too short, and the torque performance is greatly reduced. On the other hand, if the inclination of the taper of the threaded portion is too gentle, the overall length of the threaded portion increases, which increases the manufacturing cost. Therefore, it is preferable that the taper angle of the thread portion is 1.5° to 4° with respect to the pipe axis. A more preferable lower limit of the taper angle of the thread portion is 2.0°. A more preferable upper limit of the taper angle of the thread portion is 3.6°.

Preferably, the gap between the crest surface of the thread and the bottom surface of the thread groove in the thread portion is 0.10 mm or more and less than 0.20 mm. If the clearance of the threaded portion is less than 0.10 mm, the plastic deformation of the threaded portion starts early during tightening, and the load load on the shoulder portion becomes insufficient. A more preferable lower limit of the clearance of the thread portion is 0.12 mm. On the other hand, when the gap between the threaded portions is 0.20 mm or more, the sealing performance of the inner seal portion in particular decreases. A more preferable upper limit of the clearance of the thread portion is 0.16 mm. The clearance range of these screw parts is the same as the clearance of the insertion surface.

In terms of practical application, it is preferable that the threaded portion has one thread or two threads.

In addition, this invention is not limited to above-mentioned embodiment, In the range which does not deviate from the summary of this invention, various changes are possible.

In addition, each sealing surface constituting the above-mentioned surface-contact-based sealing portion (inner sealing portion and outer sealing portion) is formed together with other parts by a series of machining processes. At this time, the feed speed of the tool when machining each sealing surface is set to a lower speed than when machining other parts. As a result, each sealing surface is significantly smoother than the machined surfaces at other locations.

7 and 8 are longitudinal cross-sectional views schematically showing the region of the sealing portion by surface contact. In FIG. 7 , an inner seal portion (first seal portion) is shown as an example. In FIG. 8 , an outer seal portion (second seal portion) is shown as an example. As shown in FIG. 7 , the inner seal portion refers to a region Sa where the first seal surfaces 12 and 22 are in contact with each other in a fastened state. The length in the tube axis direction of the inner seal portion is preferably 1 mm to 7 mm. On the other hand, the first sealing surfaces 12 and 22 refer not only to the region Sa that is in contact with each other in a fastened state, but to the entire regions Sb and Sc processed to have smooth surfaces as sealing surfaces. The region Sc corresponds to the first tapered surface 12a of the male snap 10 described above. That is, the first sealing surfaces 12 and 22 are regions (including regions where there is a possibility of sliding) that slide while contacting each other during fastening, and include regions Sa that are processed to be equivalent to the regions Sa that are in contact with each other in a fastened state. The surface accuracy of the area Sb, Sc the entire area. The same applies to the outer seal portion shown in FIG. 8 .

When the male snap 10 is detached from the female snap 20 and the sealing surface is observed, the sealing portion can be recognized. The reason for this is that traces (regions that slid violently) of the sealing portion (contact region Sa in a fastened state) remain on the sealing surface.

Example

In order to confirm the effects of the present invention, numerical simulation analysis based on the elastic-plastic finite element method was carried out.

<Test conditions>

In the FEM analysis, a plurality of models of the integral type threaded joint for steel pipes shown in FIG. 1 were produced. In these models, various changes were made to the distance L1 from the inner seal portion to the shoulder portion and the distance L2 from the outer seal portion to the shoulder portion. This change changes the distance L between the inner seal portion and the outer seal portion. Furthermore, various changes have been made to the angle of the shoulder surface.

As a conventional example for comparison, the following model was produced. In the joint of the model of this conventional example, the inside seal part is provided in the front-end|tip part of a pin, and the outside seal part is provided in the front-end|tip part of a box. In addition, two stages of taper threaded parts of partial trapezoidal shape are provided in the area between the inner sealing part and the outer sealing part, and a shoulder part is provided at the boundary of the two stages of threaded parts.

The main dimensions of each model are shown in Tables 1 to 3 below. In these tables, Table 2 shows the various dimensions of the pin buckle, and Table 3 shows the various dimensions of the box buckle.

[Table 1]

Table 1

Remarks) * mark: means departing from the conditions stipulated in the present invention.

[Table 2]

Table 2

[table 3]

table 3

Other common conditions are as follows.

·Steel pipe size: 14[inch], 115[lb/ft] (outer diameter is 355.6mm, inner diameter is 314.35mm, wall thickness is 20.625mm)

Grade of steel pipe: API standard Q125 (carbon steel with a yield strength of 125ksi (862MPa))

<Evaluation method>

In the FEM analysis, loads simulating the Series A test of ISO13679 were sequentially applied to each model in the fastened state. By comparing the minimum value of the seal contact force [N/mm] of the outer seal portion (second seal portion) under this load, that is, the minimum value of “average contact surface pressure between seal surfaces” × “contact width”, for The sealing performance against external pressure was evaluated. A higher value of the contact force indicates better sealing performance of the sealing portion. Similarly, for the inner seal portion (first seal portion), the seal performance against internal pressure was evaluated by comparing the seal contact force.

<Test results>

The test results are shown in Table 4 below.

[Table 4]

Table 4

As shown in Table 4, tests No. 4 to No. 9 of the examples of the present invention satisfying all the conditions specified in the present invention, and conventional examples and comparisons of test No. 1 not satisfying any of the conditions specified in the present invention Compared with Test No. 2 and No. 3 of the example, the contact force between the outer seal part and the inner seal part was significantly improved. This tendency was similarly confirmed even if the angle of the shoulder surface was changed within the range of 75° to 95°. From this, it can be confirmed that the sealing performance against internal pressure and external pressure can be reliably improved by adopting the threaded joint for steel pipes of the present invention.

Industrial availability

The threaded joint of the present invention can be effectively used for connecting steel pipes used as oil well pipes.

Explanation of reference signs

10. Male buckle; 11. The first external thread part; 11a, the thread crest surface of the first external thread part; 11b, the bottom surface of the thread groove of the first external thread part; 11c, the insertion flank of the first external thread part; 11d, the load flank of the first external thread; 12, the first sealing surface; 12a, the first tapered surface; 12b, 12c, the first curved surface; 13, the shoulder surface; 14, the second sealing surface; 14a, 2nd cone surface; 14b, 14c, 2nd curved surface; 15, 2nd external thread part; 15a, thread crest surface of 2nd external thread part; 15b, thread groove bottom surface of 2nd external thread part; 15c, 2nd external thread part 2 The insertion flank of the external thread; 15d, the load flank of the second external thread; 20, the box; 21, the first internal thread; 21a, the top surface of the first internal thread; 21b, the first thread 1 The bottom surface of the thread groove of the internal thread part; 21c, the insertion flank of the first internal thread part; 21d, the load flank of the first internal thread part; 22, the first sealing surface; 23, the shoulder surface; 24, the second Sealing surface; 25, the second internal thread part; 25a, the thread crest surface of the second internal thread part; 25b, the bottom surface of the thread groove of the second internal thread part; 25c, the insertion flank of the second internal thread part; 25d, The load flank of the second internal thread; L, the distance between the first seal and the second seal; L1, the distance from the first seal to the shoulder; L2, the distance from the second seal to the platform The distance to the shoulder; P1, the boundary position between the first taper surface and the first curved surface on the tip side of the pin; P2, the distance between the second taper surface and the second curved surface on the tube body side of the pin Boundary position; P3, the position of the smallest diameter in the contact area between shoulder surfaces; C1, clearance; C2, clearance; CL, pipe axis.

Claims (13)

1. a kind of screw joint for steel pipe is made of the female thread of the pin thread of tubulose and tubulose, the pin thread is screwed into the mother Button is to fasten the pin thread and the female thread, in the screw joint for steel pipe,

The outer diameter of the female thread is less than the 110% of the outer diameter of the pipe main body of the pin thread,

The pin thread from the top of the pin thread towards pipe main body successively have swallowtail shape taper thread the 1st external thread part, 1st sealing surface, circular bead surface, the 2nd sealing surface and swallowtail shape taper thread the 2nd external thread part,

1st sealing surface has the 1st flexure plane at the both ends of the 1st conical surface and the 1st conical surface,

2nd sealing surface has the 2nd flexure plane at the both ends of the 2nd conical surface and the 2nd conical surface,

Until the boundary to the circular bead surface between the 1st flexure plane of the tip side of the 1st conical surface and the pin thread Tube axis direction on distance L1 be 15mm or more,

It is to the circular bead surface from the boundary between the 2nd flexure plane of the pipe main body side of the 2nd conical surface and the pin thread Distance L2 on tube axis direction only is 15mm or more,

Total distance L of the distance L1 and distance L2 is 50mm or more,

The female thread successively have from the pipe main body of the female thread towards top the taper thread of swallowtail shape the 1st internal thread part, 1st sealing surface, circular bead surface, the 2nd sealing surface and swallowtail shape taper thread the 2nd internal thread part,

Under tightening state,

The circular bead surface is in contact with each other, and the 1st sealing surface is in contact with each other, and the 2nd sealing surface is in contact with each other,

It is formed with gap between the 1st external thread part and the insertion tooth side of the 1st internal thread part, and in institute It states between the screw thread groove bottom of the 1st external thread part and the thread top surface of the 1st internal thread part or in the 1st external thread part Thread top surface and the 1st internal thread part screw thread groove bottom between be formed with gap,

It is formed with gap between the 2nd external thread part and the insertion tooth side of the 2nd internal thread part, and in institute It states between the screw thread groove bottom of the 2nd external thread part and the thread top surface of the 2nd internal thread part or in the 2nd external thread part Thread top surface and the 2nd internal thread part screw thread groove bottom between be formed with gap.

2. screw joint for steel pipe according to claim 1, wherein

The gap between the thread top surface and the screw thread groove bottom is 0.10mm more than and less than 0.20mm.

3. screw joint for steel pipe according to claim 1, wherein

In the longitudinal section along pipe axis, pipe axis and the circular bead surface angulation are 75 °~105 °.

4. screw joint for steel pipe according to claim 1, wherein

Total distance L is 90mm or less.

5. screw joint for steel pipe according to any one of claims 1 to 4, wherein

The 1st threaded portion that be made of the 1st external thread part and the 1st internal thread part and by the 2nd external thread part and The 2nd threaded portion that 2nd internal thread part is constituted is 1 article of screw thread or two articles of screw threads.

6. screw joint for steel pipe according to claim 2, wherein

In the longitudinal section along pipe axis, pipe axis and the circular bead surface angulation are 75 °~105 °.

7. screw joint for steel pipe according to claim 2, wherein

Total distance L is 90mm or less.

8. screw joint for steel pipe according to claim 3, wherein

Total distance L is 90mm or less.

9. screw joint for steel pipe according to claim 6, wherein

Total distance L is 90mm or less.

10. screw joint for steel pipe according to claim 6, wherein

The 1st threaded portion that be made of the 1st external thread part and the 1st internal thread part and by the 2nd external thread part and The 2nd threaded portion that 2nd internal thread part is constituted is 1 article of screw thread or two articles of screw threads.

11. screw joint for steel pipe according to claim 7, wherein

The 1st threaded portion that be made of the 1st external thread part and the 1st internal thread part and by the 2nd external thread part and The 2nd threaded portion that 2nd internal thread part is constituted is 1 article of screw thread or two articles of screw threads.

12. screw joint for steel pipe according to claim 8, wherein

The 1st threaded portion that be made of the 1st external thread part and the 1st internal thread part and by the 2nd external thread part and The 2nd threaded portion that 2nd internal thread part is constituted is 1 article of screw thread or two articles of screw threads.

13. screw joint for steel pipe according to claim 9, wherein

The 1st threaded portion that be made of the 1st external thread part and the 1st internal thread part and by the 2nd external thread part and The 2nd threaded portion that 2nd internal thread part is constituted is 1 article of screw thread or two articles of screw threads.